This invention pertains to the art of wheelchairs, and more particularly, to powered wheelchairs. The invention is particularly applicable to battery powered wheelchairs and will be described with particular reference thereto. It will be appreciated that the invention has broader applications and may be advantageously employed in related powered wheelchairs and not restricted to the particular embodiment described.
Present day wheelchair manufacturers all employ substantially the same type of drive mechanism for battery powered wheelchairs. Specifically, suitable connections are made between the battery and first and second drive motors. The drive motors are positioned generally parallel to side frames of the wheelchair. That is, output shafts of the drive motors are disposed substantially parallel to the side frames so that it is necessary to employ right angle gear boxes to transfer the output power of the drive motors to drive shaft and drive pulley arrangements. The driven wheels of the powered wheelchair are oriented for rotation in planes generally parallel to the side frames, i.e., rotation about axes substantially perpendicular to the side frames.
A primary reason for the "parallel" mounting of the drive motors is that development of powered wheelchairs evolved from motorizing unpowered, collapsible wheelchairs. The unpowered wheelchairs had developed to a stage in which the folding or collapsible nature was heavily emphasized for transport and storage reasons. Adapting drive motors to these wheelchairs restricted the drive motors to a parallel mounting arrangement because of the collapsible nature of the wheelchair. Wheelchair manufacturers became accustomed to this original mounting arrangement and continue to construct powered wheelchairs with a parallel mounting arrangement of the drive motors. In fact, the technological evolution of the powered wheelchairs, particularly the drive mechanism arrangement, has stagnated and resulted in concentration on other aspects of the wheelchair.
It is believed that another reason for this parallel mounting arrangement of the drive motors is aesthetics. That is, the drive motors may be more effectively "hidden" by mounting the motors in a parallel arrangement with the side frames. Also, in limited situations this arrangement of the drive motors would still permit partial collapsing of the wheelchair for ease of transportation.
Collapsing the wheelchair for ease of transportation, though, is not believed to be a viable reason for the industry's continued use of the parallel mounting of the drive motors. Since the typical powered wheelchair carries a battery, collapsing the powered wheelchair is not a primary concern. A rigid platform extends between the side frames to support the battery so that both the battery and platform would have to be removed from the wheelchair for collapsing. Thus, since a user would not contemplate repeated and ready folding of a powered wheelchair due to the cumbersome removal of the battery and platform, orientation of the drive motors is not a major factor in wheelchairs of this type.
Additionally, users of these powered wheelchairs are often quadriplegics or similarly disabled to the extent that the user and powered wheelchair are transported as a unit. Lifts are incorporated into vans, buses, etc., and the entire wheelchair clamped into secure engagement. In other words, the user never leaves the wheelchair except for sleeping and other selected activities.
Disposition of the drive motors in the parallel mounting arrangement requires a right angle gear box as indicated above and which typically uses a worm and a worm gear. Worm gearing is oftentimes used because of the large speed reductions that result from the structural arrangement. There is a large amount of sliding that results in this type of gearing and thereby results in a loss of drive motor efficiency.
The sliding in a worm gear arrangement also has an impact on the overall efficiency of power transmission from the drive motor output shaft to the drive pulley. A substantial loss is realized in the right angle gear box. Beyond the heating and noise of the drive motors, the most significant characteristic of the inefficient transmission of power from the drive motor through the gear box and to the drive pulley is realized in the reduced range with a predetermined battery charge.
The use of a right angle gear box dictates that a manufacturer maintain an inventory of right-hand and left-hand right angle gear boxes to satisfy the original manufacture and replacement parts necessary with the parallel mounting arrangement. Although the right-hand and left-hand drive motors are substantially the same, the right and left gear boxes are different. In terms of ease of manufacture, storage and inventory, it would be highly desirable to employ a more universal arrangement.
As is also customary with powered wheelchairs of this type, the battery is often located toward the rear of the chair and at an area that is fully supported by the rear-driven wheels. In addition to the weight of a battery and wheelchair user, the drive motors constitute a substantial portion of the overall weight of the assembly. As alluded to above, the drive motors are secured to the side frames and oftentimes are mounted in such a manner that the center of gravity of the entire unit is disposed toward the rear of the wheelchair. Wheelchair manufacturers employ extensions from the rear of the frame that act as anti-tip mechanisms due to the rearward disposal of the center of gravity of the unit. On inclined surfaces, the rearward disposal of the center of gravity is more apparent since the smaller diameter front wheels have a greater tendency to be raised off the ground surface. It is thus oftentimes desirable to shift the center of gravity forwardly.